1. Field of the Description
The present invention relates, in general, to devices and methods for providing a three-dimensional (3D) display in a glasses-free manner, and, more particularly, to a display system adapted for using a horizontally-oriented display (e.g., “a 3D tabletop display”) to display high quality 3D images (left and right eye images) to one or more viewers' eyes that can be viewed without the need for the viewer to use special glasses, headgear, or filters (e.g., glasses-free 3D or autostereoscopy).
2. Relevant Background
Displays that provide the illusion of three dimensions have experienced a rebirth in the past few years. For example, a number of 3D televisions are now available for use in homes and home theaters. These 3D televisions generally operate by displaying a stream of left and right eye images in an alternating or time-multiplexed manner (e.g., left-right-left-right). Switching occurs so quickly that the viewer does not sense a flicker or change in the display. The viewer wears special headgear or glasses that operate in a synchronized manner with the display to only allow the light associated with the left eye image to reach the viewer's left eye and with the right eye image to reach the viewer's right eye.
While most commercial displays rely on the use of special glasses, it is generally agreed by those in the 3D entertainment industry that displays able to provide a 3D viewing experience without glasses or headgear offer significant advantages. Autostereoscopy is any method of displaying stereoscopic images (i.e., adding binocular perception of 3D depth) without the use of special glasses or headgear on the part of the viewer. Many autostereoscopic or glasses-free 3D displays have been developed using a variety of technologies including lenticular lenses on the display screen combined with interlaced content, screens configured as parallax barriers, volumetric displays, and holographic and light field displays. However, each display technology has to date been proven to have limitations that have limited their widespread adoption.
For example, 3D televisions have been configured as lenticular autostereoscopic displays. The 3D lenticular television is mounted vertically on a wall or on a support base, and a viewer has left and right eye images directed toward their eyes through a plurality of lenticules (or elongated lenses) that extend vertically upward or in a slanted manner upward on the outer surface of the display monitor. The 3D lenticular television may provide 1920 by 1200 pixels that are used to display an 8-view autostereoscopic image through the lenticules (or lens array or lenticular sheet). To this end, the image content (or digital image file) is interdigitated or interlaced as a number of slices (e.g., 8 slices in this example) of images that include left and right eye images to provide the 3D effect, and the set of interlaced slices are displayed and repeated under each lenticule.
These 3D televisions have a number of drawbacks in practice. The viewer typically has to remain in a particular location relative to the front surface (lenticular sheet) of the display/monitor such as directly in front of the display/monitor and with their head (and left and right eyes) at a predefined height (e.g., a height matching the center of the display/monitor). The lenticular 3D television only provides views horizontally so if the viewer is at too great of a height (or too low of a height) the 3D image is viewed from an incorrect perspective, resulting in a distorted image that appears in an undesirable or unrealistic manner. The lenticular 3D television has a narrow field of view (fov), e.g., about 13 degrees, such that movement to the left or the right of the center position can result in confused (pseudoscopic) or repeated viewpoints, possibly ruining the 3D effect or correct perspective.
In either case, the interdigitated pixels or slices of the images are generated for views in a nominal view zone (e.g., assuming a viewer is located centrally in front of the display). However, due to inherent lens cross-talk, views are repeated at each of a number of additional view zones to the left and right of the nominal view zone (e.g., repeated view zones). In the example of an 8-view autostereoscopic image, eight pixels or slices are interlaced in a particular pattern (View image 0, View image 1 . . . View image 7), and this pattern is presented in each view zone. The interdigitated image sets (or sets of pixels or image slices) are chosen with the assumption that the view images are captured at a fixed distance and spacing from the front surface or lenticular sheet such as about 13 feet away. If the cameras are moved closer to the front surface or too far to the side to coincide with the viewer's viewpoints, the quality of the 3D image may quickly be unacceptable. For example, if a viewer is located such that their right eye is in the nominal view zone but their left eye is in a repeated zone, the eyes' view order will be incorrect and the viewer will perceive a pseudoscopic image with incorrect 3D cues and confused imagery. Similarly, if the eight camera's view images are captured from locations away from the nominal view distance (such as to render from a tracked viewer's eye points) but otherwise interlaced as before, the viewer's angle of convergence of the display will be incorrect leading to depth distortion. Typically, the camera separation (the stereo base line) and field of view must be adjusted to correct the depth distortion. However, this likely means that cameras will not be at the two viewer's eye points (so, incorrect perceptive), and the display will not allow for smooth parallax as camera viewpoints are constrained and will not account for repeated or straddled view zones. As a result, even with the use of tracking devices to compensate for perspective distortion in the render view images, lenticular 3D televisions (horizontally or vertically-mounted 3D displays) are limited in their effectiveness in displaying 3D imagery to a viewer that changes their height, viewing position, or changes their proximity to the display or their viewing distance.